The present invention relates to an optical module, an optical imaging device, a method for supporting an optical element, an optical imaging method, and a method for structuring a contact section of an optical module. The invention can be applied in connection with any desired optical devices and optical imaging methods. In particular, it can be used in connection with the micro lithography used in the production of microelectronic circuits.
Particularly in the field of microlithography, besides using components configured with the highest possible precision, it is necessary, inter alia, to set the position and geometry of optical modules of the imaging device, that is to say for example of the modules having optical elements such as lens elements, mirrors or gratings but also of the masks and substrates used, during operation as precisely as possible in accordance with predefined desired values or to stabilize such components in a predefined position or geometry, in order to achieve a correspondingly high imaging quality.
In the field of microlithography, the accuracy requirements are in the microscopic range of the order of magnitude of a few nanometers or less. They are not least a consequence of the constant need to increase the resolution of the optical systems used in the production of microelectronic circuits, in order to advance the miniaturization of the microelectronic circuits to be produced.
With the increased resolution and the generally accompanying reduction of the wavelength of the light used, the requirements made regarding the accuracy of the positioning and orientation of the components used naturally increase. In particular for the short operating wavelengths used in microlithography in the UV range (for example in the range of 193 nm), but in particular in the so-called extreme UV range (EUV) with operating wavelengths of between 5 nm and 20 nm (typically in the region of 13 nm), this of course affects the efforts to be made for complying with the stringent requirements made of the accuracy of the positioning and/or orientation of the components involved.
In connection with the abovementioned stabilization of the optical system, dealing with vibrational energy which arises in the system or is introduced into the system from outside proves to be particularly problematic, however. One approach often used for solving this problem consists in actively influencing the position and/or orientation of individual or a plurality of the system components used, in particular optical elements used, in order to hold the relevant component at a predefined position and/or in a predefined orientation.
DE 102 05 425 A1 (Holderer et al.), the disclosure of which is incorporated herein by reference, in connection with the defined positioning and orientation of the facet elements of a facet mirror of an EUV system, discloses individually adjusting the facet elements and then holding them in the adjusted state via corresponding fixing forces.
Although a misalignment of the facet elements as a result of introduced vibrational energy relative to the carriers thereof can be prevented in this case via correspondingly dimensioned fixing forces, what is problematic is that the carrier itself can be deformed by introduced vibrational energy, such that the facet elements can be deflected from their desired position and/or orientation in the beam path.
Moreover, active influencing of the position and/or orientation of individual or a plurality of optical elements of the imaging system is often desired in order to increase the flexibility of the optical system. In this regard, once again in the case of EUV systems, in particular in the illumination device, for flexible pupil formation it is desirable to use facet mirrors having a large number of movable (typically tiltable) micromirrors or facet elements, the respective position and/or orientation of which must then, of course, be set and held in a highly precise manner.
Particularly in the case of such EUV systems it is a particular challenge to realize the precise setting of the position and/or orientation of a large number of facet elements in conjunction with very small dimensions of the facet elements. In this regard, in the case of a facet mirror for such a EUV system, the number of facet elements is typically of the order of magnitude of several hundreds of thousands of facet elements, while the diameter of the optically effective surface of the individual facet element is typically of the order of magnitude of a several hundred micrometers.
Similar micromirror arrays comprising several hundreds of thousands of micromirrors are also known for example from U.S. Pat. No. 6,906,845 B2 (Cho et al.), the disclosure of which is incorporated herein by reference.